The present application relates to photonic devices formed with Group III nitrides, and more particularly to photonic devices formed with polarization free Group III nitrides on (100) silicon substrates.
Group III nitrides are a unique group of semiconductor materials which can be used for fabrication of visible and ultraviolet high-power and high-performance photonic devices, specifically laser diodes. Group III nitrides are composed of nitrogen and at least one element from Group III, i.e., aluminum (Al), gallium (Ga) and indium (In), of the Periodic Table of Elements. Illustrative examples of some common Group III nitrides are GaN, GaAlN, and GaAlInN. By changing the composition of Al, Ga and/or In within Group III nitrides, the emission of Group III nitrides can be tuned along the electromagnetic spectrum; mainly from 210 nm to 1770 nm.
Group III nitride-based laser diodes are highly demanded for many portable consumer devices such as handheld projectors, high resolution televisions, displays, and lighting. The challenges for making high efficiency Group III nitride-based laser diodes are numerous. First of all, Group III nitrides are typically grown epitaxially over a substrate by conventional growth techniques including molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD) or hybrid vapor phase epitaxy (HVPE). The Group III nitrides can crystalize in a hexagonal wurtzite phase or in a cubic phase. The epitaxial growth of Group III nitrides on a conventional substrate such as, sapphire or SiC, typically results in formation of wurtzite phase Group III nitrides due to higher stability of wurtzite phase. However, the wurtzite phase is not a preferred phase for laser diodes because the wurtzite phase leads to a spontaneous polarization that induces an internal electric field. Such internal electric field is often deleterious for laser diodes as the internal electric field reduces the recombination efficiency of electrons and holes and also makes it difficult to push towards the optical emission of laser diodes to longer wavelengths. Forming Group III nitrides having a cubic phase can eliminate piezoelectric fields and enhance radiative recombination dynamics as the cubic phase is non-polar and has thus no net polarization filed (i.e., polarization free). Another problem for growing high quality Group III nitride films is the lack of a suitable substrate that matches the lattice constant of the Group III nitride films. Group III nitride films heteroepitaxially grown on highly lattice-mismatched substrates such as sapphire, SiC and silicon contain high densities of defects (around 1.0×109 defects/cm2). Dry etching or polishing is thus needed to form cavity mirrors for laser radiation. However, such processes normally cause non-ideal cavity mirror formation.
Therefore, there remains a need for a method that allows growing high quality cubic phase Group III nitrides for photonic applications.